On 15/07/2016 14:15, Radim Krčmář wrote:
> 2016-07-06 15:43+0200, Paolo Bonzini:
>> I don't know what I was thinking when I wrote commit 46896c73c1a4 ("KVM:
>> svm: add support for RDTSCP", 2015-11-12); I missed write_rdtscp_aux which
>> obviously uses MSR_TSC_AUX.
>>
>> Therefore we do need to save/restore MSR_TSC_AUX in svm_vcpu_run.
>
> Hm, MSR_TSC_AUX is in host_save_user_msrs[], so we save it on every
> svm_vcpu_load() and restore on svm_vcpu_put(). Linux does not use
> RDTSCP and every transition to userspace has svm_vcpu_put() in between.
>
> We also still do "wrmsrl(MSR_TSC_AUX, svm->tsc_aux);" in svm_set_msr()
> and can switch to userspace without performing svm_vcpu_run() first.
>
> Was this patch fixing the host userspace or something in the guest?
I think I was helping someone to debug an AMD failure and missed the
addition to host_save_user_msrs in commit 46896c73c1a4. So feel free to
revert, I guess. Sorry for the mess.
Paolo
> Thanks.
>
>> Cc: stable@xxxxxxxxxxxxxxx
>> Cc: Borislav Petkov <bp@xxxxxxxxx>
>> Fixes: 46896c73c1a4 ("KVM: svm: add support for RDTSCP")
>> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>> ---
>> arch/x86/kvm/svm.c | 8 +++++---
>> 1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>> index 16ef31b87452..44f6368f8b45 100644
>> --- a/arch/x86/kvm/svm.c
>> +++ b/arch/x86/kvm/svm.c
>> @@ -43,6 +43,7 @@
>> #include <asm/kvm_para.h>
>>
>> #include <asm/virtext.h>
>> +#include <asm/vgtod.h>
>> #include "trace.h"
>>
>> #define __ex(x) __kvm_handle_fault_on_reboot(x)
>> @@ -1530,9 +1531,6 @@ static void svm_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>> wrmsrl(MSR_AMD64_TSC_RATIO, tsc_ratio);
>> }
>> }
>> - /* This assumes that the kernel never uses MSR_TSC_AUX */
>> - if (static_cpu_has(X86_FEATURE_RDTSCP))
>> - wrmsrl(MSR_TSC_AUX, svm->tsc_aux);
>>
>> avic_vcpu_load(vcpu, cpu);
>> }
>> @@ -4474,6 +4472,8 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
>> svm->vmcb->save.cr2 = vcpu->arch.cr2;
>>
>> clgi();
>> + if (static_cpu_has(X86_FEATURE_RDTSCP))
>> + wrmsrl(MSR_TSC_AUX, svm->tsc_aux);
>>
>> local_irq_enable();
>>
>> @@ -4550,6 +4550,8 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
>> #endif
>> );
>>
>> + if (static_cpu_has(X86_FEATURE_RDTSCP))
>> + wrmsrl(MSR_TSC_AUX, __getcpu());
>> #ifdef CONFIG_X86_64
>> wrmsrl(MSR_GS_BASE, svm->host.gs_base);
>> #else
>> --
>> 1.8.3.1
>>
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